While X-ray mammography has proven to be a highly sensitive clinical tool which is likely to remain as the primary method of screening for breast cancer, there is room for some significant advances in the type of information that can be presented to the clinical mammographer. Project II hypothesizes that electrical impedance spectroscopy (EIS) imaging can become a valuable clinical technique for detecting and diagnosis breast cancer by providing complementary information to that of x-ray mammography. Data in the literature has repeatedly shown that there is not only significant inherent contrast in the electrical impedance of normal and cancerous breast tissue but also that there is not only significant inherent contrast in the electrical impedance of normal and cancerous breast tissue but also that spectroscopic data can provide information on the functional status of breast tissue that could be used to diagnose benign from malignant abnormalities. Hence, while EIS may be low in overall structural imaging resolution, the high soft tissue contrast and dispersion in the electrical impedance signatures of normal and pathological tissues make a compelling argument for the potential value of EIS in terms characterizing the functional status of the imaged tissue volume through the spatially-resolved spectroscopic information that would be provided-information that is not readily available through other imaging modalities. The specific aims of Project II can be summarized as (1) to develop a multi-channel (up to 128), multi-frequency (10KHs to 5MHz), dual mode (applied current or voltage) data acquisition system and concomitant clinical electrode interface to the breast which facilitates a safe, comfortable, efficiently administered patient examine while optimizing EIS imaging performance, (2) in conjunction with the Computational ore, to develop two and three dimensional EIS image reconstruction capabilities which exploit advanced model-based image reconstruction concepts such as adaptive dual meshing, multi-component objective function minimization, parallel processing, and multi-spectral imaging, (3) to evaluate and optimize EIS imaging system performance in preclinical processing, and multis-spectral imaging, (3) to evaluate and optimize EIS imaging system performance in preclinical studies involving tissue-equivalent phantoms having geometries relevant to breast tissue imaging and (4) in collaboration with the Clinical Core, to not only demonstrate the feasibility of administering EIS breast imaging exams on human subjects but also to initiate an evaluation of the efficacy of EIS breast imaging as a diagnostic tool by correlating results with patients having normal and abnormal mammograms. The work proposed represents a unique synthesis of existing and novel ideas which should lead to important new information/documentation concerning the potential value of EIS in breast cancer detection. Not only is the scientific rationale for pursuing EIS breast imaging strong, but the practical features of (i) ease of use, (ii) low-cost and (iii) non-ionizing interrogation also make the approach extremely attractive.